Walk (@peter.naydenov/walk) ( Version 4.x.x )

Creates an immutable copies of javascript data structures(objects, arrays or mixed). Executes callback functions on every object property(object-callback) and every primitive property(key-callback). Callbacks can modify result-object during the walk process. Mask, filter or substitute values during the copy process.

const result = walk ({
                            data             // (required) Any JS data structure;
                          , objectCallback   // (optional) Function executed on each object property;
                          , keyCallback      // (optional) Function executed on each primitive property;
                    })
// Result will become a exact deep copy of "data" 
// - if callbacks are not defined
// - if callbacks are resolved with "value" without modification

Version 4 is coming with support for all primitive types including null and undefined. For simplify your migration effort here are the instructions:

• Migration guides

If you still using older versions of the library - find here the documentation:

• Documentation for walk v.3.x.x
• Documentation for walk v.2.x.x

Data structure values must be one of the following data types:

• string;
• number;
• bigint;
• boolean;
• symbol;
• null;
• undefined;
• array;
• object(data only);
• function;

Other data types can compromise the results;

keyCallback

function "keyCallback" of the walk could be used also as a deep 'forEach' method no matter of the type of the object(object or array). KeyCallback will be executed on keys that have value type: string, number, bigint, boolean, symbol, null, undefined, and function. Object and arrays will be executed only in objectCallback.

function keyCallbackFn ({value,key,breadcrumbs, IGNORE }) {
    // value: value for the property;
    // key:  key of the property;
    // breadcrumbs: location of the property;
    // IGNORE: constant. Return it if key-value pair should be ignored;
    // Callback should return the value of the property. To ignore property, return constant argument IGNORE
  }

let result = walk ({ data, keyCallback: keyCallbackFn });  // It's the short way to provide only key-callback. Callback functions are optional.
// let result = walk ({ data, keyCallback, objectCallback });  // If both callbacks are available

objectCallback

Optional callback function that is started on each object property. Function should return object or will be ignored in copy process.

function objectCallbackFn ({ value, key, breadcrumbs, IGNORE }) {
      // value: each object during the walk
      // key: key of the object
      // breadcrumbs: location of the object
      // IGNORE: Constant. Return it if key-value pair should be ignored;
      // object callback should return something.
}

let result = walk ({ data, keyCallback:keyCallbackFn, objectCallback : objectCallbackFn })

IMPORTANT: Object-callbacks are executed always before key-callbacks. If we have both callbacks, then key-callbacks will be executed on the result of object-callback.

Skip key-callbacks by not defining them:

 let result = walk ({ data, objectCallback: objectCallbackFn })   // ignore keyCallback

Installation

Install for node.js projects by writing in your terminal:

npm install @peter.naydenov/walk

Once it has been installed, it can be used by writing this line of JavaScript:

import walk from '@peter.naydenov/walk'

Versions of walk after v.3.1.x are buided as ES module, so don't forget to add type="module".

    Note:
    Library is using 'generator functions'. If support for old browsers 
    is required, add a polyfill for 'generators'.

How to use it

Deep copy

let myCopy = walk ({ data:x })   // where x is some javascript data structure

Deep 'forEach'

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };

walk ({ data:x, keyCallback : ({value,key, breadcrumbs}) => {
                  console.log (`${key} ----> ${value}`)   // Show each each primitive couples key->value
                  console.log ( `Property location >> ${breadcrumbs}`)
                  // example for breadcrumbs: 'age' will looks like this : 'root/props/age'
              }
    })

Ignore a key

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };
let result = walk ({ data:x, keyCallback : ({ value, key, IGNORE }) => {
                        if ( key === 'name' )   return IGNORE
                        return value
                })
// result will copy all properties from x without the property 'name'.
// result.name === undefined

Mask values

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 47
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };
let result = walk ({ data:x, keyCallback : () => 'xxx' })
// 'result' will have the same structure as 'x' but all values are 'xxx'
// {
//      ls    : [ 'xxx','xxx','xxx' ]
//    , name  : 'xxx'
//    , props : {
//                  eyeColor: 'xxx'
//                , age     : 'xxx'
//                , height  : 'xxx'
//                , sizes : ['xxx','xxx','xxx','xxx']
//             }
//   } 

Change object on condition

let x = {
          ls    : [ 1,2,3 ]
        , name  : 'Peter'
        , props : {
                      eyeColor: 'blue'
                    , age     : 48
                    , height  : 176
                    , sizes : [12,33,12,21]
                }
    };

function objectCallback ({ value:obj, key, breadcrumbs }) {
    const {age, height} = obj;
    if ( age && age > 30 ) {
            return { age, height }
        }
    return obj
}

let result = walk ({ data:x, objectCallback })
// 'result.props' will have only 'age' and 'height' properties.
// {
//      ls    : [ 1,2,3 ]
//    , name  : 'Peter'
//    , props : {
//                  age     : 48
//                , height  : 176
//             }
//   } 

Limitations

• walk keyCallback can return only primitives;
• walk can not execute another walk from inside of the callbacks;
• It's not recomended to use any async operations in the callbacks. Could compromise the result without any warning;

These limitations are covered in a bit larger library - walk-async. Interface is very simular but result is coming as a promise and callbacks should be resolved or rejected.

Links

• Release history
• Walk-async library

Credits

'@peter.naydenov/walk' was created and supported by Peter Naydenov.

License

'@peter.naydenov/walk' is released under the MIT License.